Step 1: Gather Items

Gather one "Pentel Wow! bk440" pen and a random pen that uses a spring.
Someone to prank.

Step 2: Dissasemble The Pens

This should come natural to you, you should be a hacker !

While doing this you should make sure that you separate the pieces so you know which goes in to the "Pentel Wow! bk440' pen case in the next step.

Step 3: Insert Spring

So, seeing that you've come this far I'll show you how to do this. Take the spring from the random pen and drop it into the "Pentel Wow ! bk440" pen case.

Step 4: Assemble Pen

Assemble the pen the way you found it, by dropping in the ink cartridge and and pushing the clicky-thingy back in.

Step 5: How To Prank Someone With The Pen

Give somebody, preferably a person that wouldn't mind a nudge of humor, the pen and ask them how to disassemble the pen. If you built it correctly the button, ink cartridge, and second spring should shoot out at them.